The installation of the damp proof course is a key stage of the building process, and one which really needs to be handled with care and attention to detail. Any faults with the installation, leading to damp ingress at a later stage, can be very expensive and difficult to fix. We recommend that only high quality damp proofing membranes that meet British Standards, and other building accreditations, should be used as it is simply not worth the risk of using lower grade product for this essential function.
Approved Document C of the Building Regulations 2000, published 28 April 2006, sets out the requirements for site preparation and resistance to contaminates and moisture - this can be seen on-line by clicking the link below. Various methods of damp proofing for different types of construction are illustrated and documented, and they provide a good general guide to understanding what will need doing for your project - Approved Document 'C'.
The Damp Proof Membrane (DPM) must be installed in conjunction with the Damp Proof Course (DPC) in the outer walls so as to form a continuous layer. Where it is necessary to join sheets of the DPM, first make sure that the surfaces to be joined are clean and free of moisture. Overlap the sheets by at least 4 to 6" (100 to 150mm) and use a double sided butyl tape or mastic strip compound to join the sheets together to form a continuous waterproof barrier. The exposed overlap joints can then be sealed using 4" (100mm) jointing tape. If any area of the DPM is damaged during installation this should be patched by overlaying a fresh piece of DPM to cover the damaged area and to overlap by at least 6" (150mm) in all directions. Once again use double-sided mastic strip, or butyl tape to create a waterproof barrier, and then seal down the edges with jointing tape.
The damp proof membrane should normally be covered with a layer of soft sand to act as a protection and to prevent damage when the concrete flooring or screed are installed.
Jackson Building Centres supply a complete range of damp proof course and damp proof membranes, including special membranes for use in areas with requirements for installation of Radon and other protective barriers.